What is the fallacy called, when discussing two opposing points of view, where one person tries to exploit the gap the other person's knowledge to try and prove their own point?

i.e. When Zack and Yvonne are debating a claim, Yvonne might ask something about it which Zack does not know the answer to (or admit that nobody knows the answer to), and then seize the doubt to push her own counter-claim.

The most common example I've come across is along the lines of:

Yvonne: God must have created the universe because there's no way it could have just come into existence out of nothing by itself.

Zack: The universe was created at the "Big Bang". All energy and matter was contained in a single point and underwent a sudden expansion which created all the elements we have today.

Yvonne: But how did the energy get there? And what was before the Big Bang?

Zack: We don't know.

Therefore, Yvonne believes, God must have put it there as it's the only other explanation.

  • 1
    I know it doesn't matter for the question, really, but I do note that the conversation works just as well in the opposite direction: Zack questions Yvonne on something, Yvonne answers with "God didn't tell us" or something along the lines that is equivalent to "We don't know", then Zack concludes her theory is false.
    – kutschkem
    Aug 2, 2022 at 11:44
  • There is a miscommunication here that is all. Yvonne here is saying Zack is inconsistent. How can Zack say something else with no cause created the universe when he just denied such a claim? If Zack denies God created the universe because a lack of knowledge then his answer to the creation problem will suffer the same critique.
    – Logikal
    Aug 2, 2022 at 12:08
  • Yvonne's first statement is an Argument from Incredulity. Aug 2, 2022 at 12:15
  • @Logikal In this example, I don't think Zack ever denied that something with no cause could create the universe; just that the universe as we know it has a traceable cause. It still leaves the question of "what caused that cause?", but Zack didnt even use that as a reason to dismiss Yvonne.
    – JMac
    Aug 2, 2022 at 15:47
  • This is a type of argumentum ad ignorantiam. The specific example you gave is known as god of the gaps, "a theological perspective in which gaps in scientific knowledge are taken to be evidence or proof of God's existence".
    – Conifold
    Aug 3, 2022 at 3:43

4 Answers 4


A fallacy is a problem in the logical structure of an argument. Where an argument is an implication, where the conclusion follows from it's premise. This isn't really the form so fallacies don't really apply here.

But if you were to rephrase it's it's probably a false dilemma. Meaning you make the tacit assumption that there are only 2 options so if it's not one it's the other, but there are infinitely many options so just ruling out one or even just expressing doubt does not confirm "the other" because it's not the only other.


It seems you might have two separate fallacies at play; one is from the question you pose, and the other is from the scenario.

What is the fallacy that claims a hypothesis/theory is false because we don't know something about it?

In other words, your claim is false, because we don't know it's true! This sounds like argument from ignorance:

Argument from ignorance (from Latin: argumentum ad ignorantiam), also known as appeal to ignorance (in which ignorance represents "a lack of contrary evidence"), is a fallacy in informal logic. It asserts that a proposition is true because it has not yet been proven false or a proposition is false because it has not yet been proven true. This represents a type of false dichotomy in that it excludes the possibility that there may have been an insufficient investigation to prove that the proposition is either true or false. It also does not allow for the possibility that the answer is unknowable, only knowable in the future, or neither completely true nor completely false.

But, I would say that the argument you present is actually an argument based on the principle of sufficient reason:

The principle of sufficient reason states that everything must have a reason or a cause. The principle was articulated and made prominent by Gottfried Wilhelm Leibniz, with many antecedents...

If one uses the principle of sufficient reason about the origins of an organized, physical universe, and then infers with logic a priori a creator necessarily exists, then such an argument might be an example of an ontological argument:

An ontological argument is a philosophical argument, made from an ontological basis, that is advanced in support of the existence of God. Such arguments tend to refer to the state of being or existing. More specifically, ontological arguments are commonly conceived a priori in regard to the organization of the universe, whereby, if such organizational structure is true, God must exist

For more information on the latter read Should the Ontological Argument be called something else than 'Ontological'? (PhilSE)


The fallacy here is the tacit assumption, that there are hypotheses/theories about which we know 'everything'.

These do not exist. Every theory comprises a certain set of 'givens' that in the framework of the theory are considered fixed and which are not subject to predictions from the theory. These 'givens' are the kernel of what we 'do not know' in the context of the theory, ie. aspects that the theory does not explain.

This is a universal property insofar as every 'explanation' means a systematic reduction of phenomena to some 'givens', which obviously must end at some point unless there is a circular reasoning.

This even applies to theories in strictly formalized and purely abstract domains, ie. in mathematics (and logic, if one regards them as different domains).

The example from the question is kind of a cheat by bringing in God as a principle which observables can be reduced to but which in itself does not need an explanation as it is deemed self-explanatory or unfathomable. Obviously this is as much of a black box as the postulates of the Big Bang theory and to establish a difference requires 'believing' in God (ie. 'no questions asked') which is purely conventional.


The example provided is an argument from ignorance, although there are a variety of other fallacies that can also apply, as fallacies tend to bleed into each other, and people often commit multiple fallacies at the same time. It is not presented as an argument explicitly, as is the case in most non-formal discussion, but what Yvonne is implicitly saying is:

  1. I have a speculation A about the reason for X
  2. You have presented no alternative explanations, or evidence against A
  3. Therefore A must be true.

The assertion that 2) leads to 3) is a classic argument from ignorance.

It ALSO can be characterized as a shifting of the burden of "proof" (we can almost never "prove" things, this should be renamed the "burden of support").

Also, hidden in Yvonne's thinking is likely to be a false dichotomy, where A or B must be the explanation, and if no B can be identified or supported, then A must be the explanation, no matter how weak its support may be. Yvonne likely has some support or justification in her head, which she has not presented, which make her think that A is plausible.

Note, false dichotomy thinking is to some extent reinforced by someone getting trained in classical logic, where only two states, true or false, can apply to a claim. We have realized that for most questions, we need at least three logic states -- true, false, and uncertain. An empiricism operates off a four state logic, of "sufficiently supported", "sufficiently contradicted", "currently indeterminate vs support or contradiction", and "poorly formed claim, cannot be evaluated". Whether the universe was caused or not, and if so what caused it, is an empirical question, and empiricism's 4 state logic applies to it.

There are other ways one may "exploit a gap in the other person's knowledge", and that is to argue in bad faith. If one knows that an evidence or argument has factual or fallacious errors to it, BUT that one's disputant does not realize this, and presents those evidences or facts anyway, that is to argue in bad faith. Philosophy SHOULD be a search for truth, not an effort to convince of a conclusion. One of the most notorious examples of bad faith argumentation is to quote-mine -- taking a quote out of context that implies the speaker supports a conclusion, fact, or POV that is very different form their actual views. Quote-miners know they are presenting false claims in bad faith, and unless the disputant know the full context of the quote, they are in a position of ignorance about the bad faith behavior of the quote-miner.

As a significant side note there are limits to the application of "fallacy" labeling to arguments and justifications. ALL justifications for a POV will eventually run afoul of the Munchausen Trilemma. The chain of justifications for any justification will eventually terminate in one of three "fallacies". Unless one wants to abandon the ability to reason and acquire knowledge, then one must have tolerance for a degree of insufficient justifications.

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